For example, as a constant velocity universal joint used as means for transmitting a rotational force at a constant velocity from an engine of an automobile to wheels, there is a tripod type constant velocity universal joint. The tripod type constant velocity universal joint has a structure capable of coupling the two shafts on the driving side and the driven side to each other, transmitting rotational torque at a constant velocity even when each of the two shafts forms an operating angle, and allowing relative displacement in an axial direction.
As the tripod type constant velocity universal joint of this type, there have been well-known one of a single-roller type in which one roller is provided as a torque transmitting member, and one of a double-roller type in which two rollers are provided so that vibration at the time of operation can be reduced. FIGS. 9 to 11 exemplify a tripod type constant velocity universal joint of the double-roller type (for example, refer to Patent Literature 1).
The tripod type constant velocity universal joint includes, as illustrated in FIGS. 9 and 10, a main portion formed of an outer joint member 110, a tripod member 120, and roller units 130 as torque transmitting members. One of the two shafts on the driving side and the driven side is coupled to the outer joint member 110, and another of the two shafts is coupled to the tripod member 120.
The outer joint member 110 is formed into a cup-like shape open at one end, and has an inner peripheral surface equiangularly provided with three linear track grooves 112 extending in an axial direction and roller-guide surfaces 114 extending in the axial direction on both sides of each of the track grooves 112. The outer joint member 110 incorporates the tripod member 120 and the roller units 130. The tripod member 120 includes three journals 122 each projected into a radial direction, and a shaft 140 is press-fitted into a center hole 128 of the tripod member 120 and spline-fitted thereto. An annular snap ring 142 prevents the shaft 140 from dropping off from the center hole 128 of the tripod member 120.
Further, each of the roller units 130 includes a main portion formed of an outer roller 132, an inner roller 134 arranged on an inside of the outer roller 132 and externally fitted to corresponding one of the journals 122, and needle rollers 136 interposed between the outer roller 132 and the inner roller 134. The roller units 130 are accommodated in the track grooves 112 of the outer joint member 110. Note that, an inner peripheral surface of the inner roller 134 has a convex circular-arc shape. As illustrated in FIGS. 9 and 10, ring-like washers 135 and 137 prevent the needle rollers 136 from being detached from each of the roller units 130 onto a shaft side or an inner surface side of the outer joint member 110.
Meanwhile, each of the journals 122 of the tripod member 120 has a straight shape orthogonal to an axial line of the joint in vertical cross-section with respect to an axial line of each of the journals 122. Further, as illustrated in FIG. 11, each of the journals 122 has a substantially elliptical shape of being held in contact with the inner roller 134 in a direction orthogonal to the axial line of the joint in lateral cross-section with respect to the axial line of each of the journals 122, and gaps m are formed between each of the journals 122 and the inner roller 134 in an axial-line direction of the joint. The roller units 130 are supported rotatably around the journals 122 each having such a shape.
In this constant velocity universal joint, the journals 122 of the tripod member 120 and the roller-guide surfaces 114 of the outer joint member 110 are engaged with each other into rotational directions of the two shafts through intermediation of the roller units 130. In this way, rotational torque is transmitted at a constant velocity from the driving side to the driven side. Further, when the roller units 130 roll on the roller-guide surfaces 114 while being rotated with respect to the journals 122, relative axial displacement and angular displacement between the outer joint member 110 and the tripod member 120 are cancelled.
In this case, the journals 122 are tiltable with respect to the roller units 130 rolling on the roller-guide surfaces 114. Thus, an attempt is made to avoid a state in which the roller units 130 and the roller-guide surfaces 114 are diagonal with respect to each other in accordance with the tilting of the journals 122 so that induced thrust and sliding resistance are reduced.